【编程练习】快速排序，Java和Python实现

Java实现

public class QuickSort {

    public static void sort(int[] a) {
        sort(a, 0, a.length-1);
    }

    public static void sort(int[] a, int lo, int hi) {
        if (lo >= hi) return;
        int j = partition(a, lo, hi);
        sort(a, lo, j - 1);
        sort(a, j + 1, hi);
    }

    public static int partition(int[] a, int lo, int hi) {
        int value = a[lo];
        int i = lo;
        int j = hi+1;
        while (true) {
            while (a[++i] <= value) {
                if (i == hi){
                    break;
                }
            }
            while (a[--j] >= value) {
                if (j == lo){
                    break;
                }
            }
            if (i>=j){
                break;
            }
            exch(a, i, j);
        }
        exch(a,lo,j);
        return j;
    }
    public static void exch(int[] a, int i, int j){
        int temp = a[i];
        a[i] = a[j];
        a[j] = temp;
    }
    public static void main(String[] args) {
        // 测试
        int[] a = {3,7,5,2,4};
        sort(a);
        for (int i:a){
            System.out.println(i);
        }
    }

}

Python实现

# -*- coding: utf-8 -*-

 # 利用缺省参数实现函数重载  
def sort(a, lo = None, hi = None):
    if lo is None and hi is None:
        sort(a, 0, len(a)-1)
        return;
    if lo is None or hi is None:
        print 'error'
        return;

    if lo >= hi:
        return;
    j = partition(a, lo, hi)
    sort(a, lo, j-1)
    sort(a, j+1, hi)

# 切分    
def partition(a, lo, hi):
    value = a[lo]

    while True:
        i = lo + 1
        j = hi
        while a[i] <= value and i <= hi:
            i += 1
        while a[j] >= value and j > lo:
            j -= 1
        if i >= j:
            break
        a[i],a[j] = a[j], a[i]  # 交换两个元素的位置
    a[lo], a[j] = a[j], a[lo]
    return j

if __name__ == "__main__":
    a = [3,7,5,2,4]
    sort(a)
    print a